Method and Device for Timing Correction in a Channel Access using a Listen-Before-Talk Protocol

ABSTRACT

According to some embodiments, a wireless device maintains timing associated with uplink transmissions by performing steps for each of a plurality of scheduled LBT transmission opportunities. The steps include determining whether an error in a current uplink transmission timing, with respect to a reference point based on a down-link timing for a reference cell, exceeds a predetermined threshold and adjusting the timing associated with uplink transmissions, for each scheduled LBT transmission opportunity for which the error exceeds the predetermined threshold. The steps also include performing an LBT assessment to determine whether the wireless device is permitted to transmit in the scheduled LBT transmission opportunity and, for each scheduled LBT transmission opportunity in which the LBT assessment indicates that the wireless device is not permitted to transmit, reversing any adjustment to the timing associated with uplink transmissions made for that scheduled LBT transmission opportunity.

TECHNICAL FIELD

The present invention generally relates to wireless communicationnetworks, and particularly relates to transmission timing when usingunlicensed frequency bands.

BACKGROUND

Long Term Evolution (LTE) specifications support Component Carrier (CC)bandwidths up to 20 MHz (the maximum LTE Rel-8 carrier bandwidth). LTEoperation with wider bandwidth than 20 MHz is possible, using multipleCCs, appearing as a number of LTE carriers to an LTE terminal. Astraightforward way to obtain this would be by means of CarrierAggregation (CA). The LTE standard supports up to five aggregatedcarriers, where each carrier is limited, according to the 3GPPspecifications, to have one of six bandwidths, namely 6, 15, 25, 50, 75or 100 RB (corresponding to 1.4, 3, 5, 10, 15 and 20 MHz respectively).The number of aggregated CCs as well as the bandwidth of the individualCC may be different for uplink and downlink.

During initial access, an LTE CA-capable terminal behaves similarly to aterminal not capable of CA. Upon successful connection to the network, aterminal may, depending on its own capabilities and the network, beconfigured with additional CCs in the uplink (UL) and downlink (DL).This configuration is based on Resource Radio Control (RRC) signaling.Due to the heavy signaling and rather slow speed of RRC signaling, it isenvisioned that a terminal may be configured with multiple CCs, evenwhen not all of them are currently used.

In CA, the terminal (user equipment or UE) is configured with a primaryCC (PCC), a primary cell (PCell) or a primary serving cell (PSC). ThePCell is particularly important, e.g., due to control signaling on thiscell and UE monitoring of the radio quality on the PCell. A CA-capableterminal can, as explained above, also be configured with additionalcarriers (or cells or serving cells) which are referred to as secondaryCCs (SCC), secondary cells (SCell) or secondary serving cells (SSC).Note that these terms may be used interchangeably.

To further improve the performance of LTE systems, CA has been expandedto enable the use of LTE in an unlicensed spectrum. This operation isreferred to as Licensed Assisted Access (LAA). Since unlicensed spectrummay never match the qualities of licensed spectrum, the intention withLAA is to apply carrier aggregation and use a secondary carrier in anunlicensed band, while having a primary carrier in a licensed band. Thiswill then ensure that the reliability associated with licensed carrierscan be enjoyed for the primary carrier and only secondary carriers areused in unlicensed bands. However, operation of unlicensed carrier asstandalone operation or CA with a primary carrier in an unlicensed bandmay also be employed. CA using licensed and unlicensed carriers isshown, for example, in FIG. 1.

According to 3GPP specifications under development, frame structure type3 (FS3) is applicable to LAA secondary cell operation. In FS3, a radioframe is 10 milliseconds (ms) long and consists of 10 frames, each of 1ms. Each subframe has two slots, each with a length of 0.5 ms. InRelease 13 of the 3GPP specifications, all 10 subframes within a radioframe are for downlink transmissions. With LAA operation in uplink, theframe structure may introduce new configurations containing a mixture ofdownlink and uplink subframes in a radio frame.

In Dual Connectivity (DC) operation, the UE can be served by at leasttwo nodes called master eNB (MeNB) and secondary eNB (SeNB). Moregenerally, in multiple connectivity (multi-connectivity or MC)operation, the UE can be served by two or more nodes, such as an MeNB,SeNB1, SeNB2 and so on. The UE is configured with a primary componentcarrier (PCC) from both MeNB and SeNB. The primary cell (PCell) fromMeNB and SeNB are called PCell and primary secondary cell (PSCell),respectively. The PCell and PSCell typically operate the UEindependently. The UE is also configured with one or more secondarycomponent carriers (SCCs) from each of MeNB and SeNB. The correspondingsecondary serving cells served by MeNB and SeNB are called secondarycells (SCells). The UE in DC typically has separatetransmission/reception for each of the connections with MeNB and SeNB.This allows the MeNB and SeNB to independently configure each UE withone or more procedures, such as radio link monitoring (RLM), DRX cycle,etc., on its PCell and PSCell, respectively.

In order to transmit in unlicensed spectrum, which is free and shared byeveryone, some regulations have to be followed. Most regulatory bodies,including Europe's ETSI, require networks operating in unlicensedspectrum to use a Carrier Sense Multiple Access (CSMA) protocol. Thismeans that transmitters are required to listen to the presence ofcarriers in the channel (or a time resource such as a symbol, time slot,frame, subframe, etc.) before occupying the channel and transmitting fora particular duration. This is performed by detecting energy on thatparticular channel for a channel sensing duration. Hence, this protocolis also known as Listen-Before-Talk (LBT) protocol.

Due to LBT, a transmission in an unlicensed band may be delayed untilthe medium becomes free again. In a case where there is no coordinationbetween the transmitting nodes (which often is the case), the delay mayappear random. More specifically, the transmitter node determineswhether the channel is free or occupied by measuring the energy on themedium over a certain duration, i.e., an LBT measurement duration. Ifthe channel is found to be free, the transmitter occupies the channeland can transmit during a channel occupancy time, which can extend overa certain number of time resources, such as between 4 ms and 10 ms. Ifthe channel is found to be occupied, on the other hand, the transmitternode refrains from transmitting and waits until the channel becomesfree.

To determine whether the channel is occupied or not during a particularLBT duration, a transmitter measures the energy detected during the LBTmeasurement duration and computes the corresponding power level. Thepower level is compared against a carrier sensing threshold, which maybe referred to as an LBT threshold. If the power level is above thecarrier sensing threshold, the channel is considered to be occupied. Onthe other hand, if the power level is below the threshold, then thechannel is considered to be free.

The LBT procedure may also be called a channel-carrier-sensemultiple-access (CSMA) scheme, a channel assessment scheme, aclear-channel assessment scheme, etc. The CSMA or LBT based operation ismore generally referred to as contention-based operation. Thiscontention-based operation is typically used for transmission oncarriers of an unlicensed band. However, this mechanism may also beapplied for operating on carriers belonging to licensed bands, forexample, to reduce interference.

According to 3GPP TS 36.133 v13.2.0, the UE is required to update oradjust the uplink transmission timing based on some rules. The intent isto ensure that the uplink transmission timing does not drift in time, asthat would result in difficulties in decoding the transmission at theeNB, or interference may even arise. The details of the uplinktransmission timing adjustments are defined as follows (from 3GPP TS36.133 v13.2.0):

7.1 UE Transmit Timing

7.1.1 Introduction

The UE shall have capability to follow the frame timing change of theconnected eNodeB. The uplink frame transmission takes place(N_(TA)+N_(TA offset))×T_(s) before the reception of the first detectedpath (in time) of the corresponding downlink frame from the referencecell. The UE shall be configured with a pTAG containing the PCell. ThepTAG may also contain up to four SCells, if configured. The UE capableof supporting multiple timing advances may also be configured with oneor two serving cells with uplink in one or two sTAG and pTAG.

The other downlink SCell(s), if configured, will be contained in eitherthe pTAG or the sTAG(s). In pTAG, the UE shall use the PCell as thereference cell for deriving the UE transmit timing for cells in thepTAG. When the UE capable of supporting multiple timing advance isconfigured with one or two sTAG(s), the UE shall use an activated SCellfrom the sTAG for deriving the UE transmit timing for cells in the sTAG.UE initial transmit timing accuracy, maximum amount of timing change inone adjustment, minimum and maximum adjustment rate are defined in thefollowing requirements. The requirements in clause 7 apply to all TAGs.

The UE capable of supporting dual connectivity shall be configured withone pTAG and may also be configured with one psTAG. The pTAG shallcontain the PCell and may also contain one SCell, if configured. ThepsTAG shall contain the PSCell and may also contain one SCell, ifconfigured. In pTAG, the UE shall use the PCell as the reference cellfor deriving the UE transmit timing for pTAG, and in psTAG, the UE shalluse the PSCell as the reference cell for deriving the UE transmit timingfor psTAG. UE initial transmit timing accuracy, maximum amount of timingchange in one adjustment, minimum and maximum adjustment rate aredefined in the following requirements. The requirements in clause 7apply to both TAGs.

7.1.2 Requirements

The UE initial transmission timing error shall be less than or equal to±T_(e) where the timing error limit value T_(e) is specified in Table7.1.2-1. This requirement applies when it is the first transmission in aDRX cycle for PUCCH, PUSCH and SRS or it is the PRACH transmission. Thereference point for the UE initial transmit timing control requirementshall be the downlink timing of the reference cell minus (N_(TA) _(_)_(ref)+N_(TA offset))×T_(s). The downlink timing is defined as the timewhen the first detected path (in time) of the corresponding downlinkframe is received from the reference cell. N_(TA) _(_) _(Ref) for PRACHis defined as 0. (N_(TA) _(_) _(Ref)+N_(TA offset)) (in T_(s) units) forother channels is the difference between UE transmission timing and thedownlink timing immediately after when the last timing advance in clause7.3 was applied. N_(TA) _(_) _(Ref) for other channels is not changeduntil next timing advance is received.

TABLE 7.1.2-1 T_(e) Timing Error Limit Downlink Bandwidth (MHz) T_(e)_(—) 1.4 24 * T_(S) ≥3 12 * T_(S) Note: T_(S) is the basic timing unitdefined in TS 36.211

When it is not the first transmission in a DRX cycle or there is no DRXcycle, and when it is the transmission for PUCCH, PUCCH and SRStransmission, the UE shall be capable of changing the transmissiontiming according to the received downlink frame of the reference cellexcept when the timing advance in clause 7.3 is applied. The UE isrequired to adjust its timing to within ±T_(e) in a TAG when,

-   -   changing the downlink SCell for deriving the UE transmit timing        for cells in the sTAG configured with one or two uplinks,    -   in this TAG the transmission timing error between the UE and the        reference timing exceeds ±Te,    -   configured with a pTAG and one or two sTAG, the transmission        timing difference between TAGs does not exceed the maximum        transmission timing difference (i.e., 32.47 us) after such        adjustment.

If the transmission timing difference after such adjustment is biggerthan the maximum transmission timing difference (i.e., 32.47 us), the UEmay stop adjustment in this TAG. The reference timing shall be (N_(TA)_(_) _(Ref)+N_(TA offset))×T_(s) before the downlink timing of thereference cell. All adjustments made to the UE uplink timing under theabove mentioned scenarios shall follow these rules:

-   -   1) The maximum amount of the magnitude of the timing change in        one adjustment shall be Tq seconds.    -   2) The minimum aggregate adjustment rate shall be 7*TS per        second.    -   3) The maximum aggregate adjustment rate shall be Tq per 200 ms.    -   where the maximum autonomous time adjustment step Tq is        specified in Table 7.1.2-2.

TABLE 7.1.2-2 T_(q) Maximum Autonomous Time Adjustment Step DownlinkBandwidth (MHz) T_(q) _(—) 1.4 17.5 * T_(S)  3 9.5 * T_(S) 5 5.5 * T_(S)≥10 3.5 * T_(S) Note: T_(S) is the basic timing unit defined in TS36.211

SUMMARY

With the introduction of LAA, the UE may be required to perform LBTbefore performing uplink transmissions, and hence the uplinktransmission timing adjustment requirements defined in 3GPP TS 36.133v13.2.0 would no longer be suitable. In particular, the UE behaviorregarding UE transmit timing adjustment is undefined and unknown in ascenario when the UE is configured or scheduled to transmit uplinksignals but it cannot transmit, for example, due to channelinaccessibility or LBT failure. The UE behavior in terms of transmittiming adjustment is also unclear if there is LBT failure in both uplinkand downlink on a carrier while the UE is scheduled or configured totransmit in the uplink.

To address these problems, various embodiments described herein aredirected to how a UE performs uplink transmission timing adjustments inscenarios where the UE operates on at least one carrier for which UEtransmissions may be dropped from time to time, such as due to LBTprocedure outcomes.

According to some embodiments, a method, in a wireless device, formaintaining timing associated with uplink transmissions includes, foreach of a plurality of scheduled LBT transmission opportunities:determining whether an error in a current uplink transmission timing,with respect to a reference point based on a downlink timing for areference cell, exceeds a predetermined threshold and adjusting thetiming associated with uplink transmissions, for each scheduled LBTtransmission opportunity for which the error exceeds the predeterminedthreshold. The method also includes performing an LBT assessment foreach of the plurality of scheduled LBT transmission opportunities, todetermine whether the wireless device is permitted to transmit in thescheduled LBT transmission opportunity, and, for each scheduled LBTtransmission opportunity in which the LBT assessment indicates that thewireless device is not permitted to transmit, reversing any adjustmentto the timing associated with uplink transmissions made for thatscheduled LBT transmission opportunity.

According to some embodiments, a method, in a wireless device, formaintaining timing associated with uplink transmissions includes, foreach of a plurality of scheduled LBT transmission opportunities:determining whether an error in a current uplink transmission timing,with respect to a reference point based on a downlink timing for areference cell, exceeds a predetermined threshold and, for eachscheduled LBT transmission opportunity for which the error exceeds thepredetermined threshold, selectively adjusting the timing associatedwith uplink transmissions, based on an estimated likelihood of LBTsuccess. The method also includes performing an LBT assessment for eachof the plurality of scheduled LBT transmission opportunities, todetermine whether the wireless device is permitted to transmit in thescheduled LBT transmission opportunity. The method may also include, foreach scheduled LBT transmission opportunity in which the LBT assessmentindicates that the wireless device is not permitted to transmit,reversing any adjustment to the timing associated with uplinktransmissions made for that scheduled LBT transmission opportunity.

The method may also be implemented by apparatus, devices, computerreadable medium, computer program products and functionalimplementations. For instance, an example wireless device according tosome embodiments is adapted to carry out one or more of the methodssummarized above, or variants thereof. Thus, some embodiments of awireless devices are adapted to, for each of a plurality of scheduledLBT transmission opportunities: determine whether an error in a currentuplink transmission timing, with respect to a reference point based on adownlink timing for a reference cell, exceeds a predetermined threshold;adjust timing associated with uplink transmissions, for each scheduledLBT transmission opportunity for which the error exceeds thepredetermined threshold; perform an LBT assessment to determine whetherthe wireless device is permitted to transmit in the scheduled LBTtransmission opportunity; and, for each scheduled LBT transmissionopportunity in which the LBT assessment indicates that the wirelessdevice is not permitted to transmit, reverse any adjustment to thetiming associated with uplink transmissions made for that scheduled LBTtransmission opportunity.

Other embodiments of a wireless device are adapted to, for each of aplurality of scheduled uplink transmission opportunities: determinewhether an error in a current uplink transmission timing, with respectto a reference point based on a downlink timing for a reference cell,exceeds a predetermined threshold; and, for each scheduled LBTtransmission opportunity for which the error exceeds the predeterminedthreshold, selectively adjust the timing associated with uplinktransmissions, based on an estimated likelihood of LBT success.

In some embodiments of a wireless device configured to maintain timingassociated with uplink transmissions, any one or more of the techniquessummarized above are carried with a processing circuit configured toperform the operations described above, e.g., using program codeorganized into functional modules corresponding to some or all of theoperations summarized above.

The described methods may be implemented in a UE by means of feedbacksignaling from an LBT entity implemented in the UE to an uplinktransmission timing adjustment entity also implemented in the UE.

Of course, the present invention is not limited to the above featuresand advantages. Those of ordinary skill in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating carrier aggregation with licensed andunlicensed frequency bands.

FIG. 2 is a block diagram of a network node configured to determinewhether a wireless device has adjusted its transmit timing, according tosome embodiments.

FIG. 3 is a block diagram of a user equipment configured to maintaintiming associated with uplink transmissions, according to someembodiments.

FIG. 4 illustrates a method of maintaining timing associated with uplinktransmissions, according to some embodiments.

FIG. 5 illustrates another method of maintaining timing associated withuplink transmissions, according to some embodiments.

FIG. 6 is a block diagram illustrating a functional implementation of awireless device configured to maintain timing associated with uplinktransmissions, according to some embodiments.

FIG. 7 is another block diagram illustrating a functional implementationof a wireless device configured to maintain timing associated withuplink transmissions, according to some embodiments.

FIG. 8 illustrates another method of maintaining timing associated withuplink transmissions, according to some embodiments.

FIG. 9 illustrates another method of maintaining timing associated withuplink transmissions, according to some embodiments.

FIG. 10 is another block diagram illustrating a functionalimplementation of a wireless device configured to maintain timingassociated with uplink transmissions, according to some embodiments.

DETAILED DESCRIPTION

Various embodiments described herein relate to when a UE is configuredwith at least one serving cell in which a channel access mechanism (e.g.LBT) is applied in order to decide whether the signals can betransmitted or not. The LBT can be applied in downlink by the networknode and/or in uplink by the UE. Various embodiments also relate to whena UE is configured with a plurality of serving cells, such as in carrieraggregation (CA), multi-connectivity (MC), etc. For example, a UE can beserved by a PCell and one or more SCells; a PCell and a PSCell; or aPCell, PSCell and one or more SCells. The embodiments described hereinare applicable to CA, DC and MC.

When a UE is operating on at least one serving cell belonging to acarrier requiring a contention-based operation, the UE, beforetransmitting on uplink, is required to check whether the channel is freeor not. The contention-based transmission is typically required inunlicensed bands but it can also be used in licensed bands. For example,the UE is required to perform an LBT procedure before deciding totransmit in uplink. During this procedure, the UE will sense the channelto determine whether some other entity is transmitting on the channel.This may be determined based on an energy-level of the channel beingbelow a threshold. For example, if the energy-level is below athreshold, the UE would consider the channel to be free (empty orclear). While if the energy-level is above a threshold, the UE wouldconsider the channel to be occupied/busy. If the channel is consideredto be busy, the UE would not be able or allowed to transmit. But if thechannel is considered free, the UE would be allowed to perform thetransmission.

If existing solutions are applied, then the UE may adjust its uplinktiming for the transmission each time such a transmission is scheduled.For example, according to existing solutions, the UE may might adjust atiming when an uplink transmission is scheduled, even when it turns outthat the UE cannot transmit due to UE LBT failure. It should beappreciated that the present 3GPP specifications for uplink timingadjustments put limits on how large an adjustment may be made at anygiven transmission opportunity. If uplink transmit timing adjustmentsare made at each LBT transmission opportunity, without regards towhether a transmission is made, the result may be that severaladjustments of the maximum size may be made in a row, without any ofthose adjustments actually being “seen” by the eNB at the other end ofthe link. When a transmission ultimately occurs, the eNB may then see achange in uplink timing that is much larger than expected which mayresult in the eNB failing to receive and decode the transmission.

The embodiments described herein, then, are directed to how a UEperforms autonomous uplink transmission timing updates when operating oncarriers in unlicensed spectrum.

Some embodiments described herein assume LBT operation is applied by theUE on an uplink serving cell. Also, these embodiments are described foroperation on carriers of an unlicensed band (e.g., LAA carriers).However, all of these embodiments are applicable to any kind of channelaccess or CSMA mechanism performed on licensed carriers or unlicensedcarriers.

FIG. 2 illustrates a network node 30. The network node 30 facilitatescommunication between UEs and the core network. The generic terminology“network node” is used, but the network node 30 can be any kind ofnetwork node such as a radio network node such as base station, radiobase station, base transceiver station, base station controller, networkcontroller, evolved Node B (eNB), Node B, Multi-cell/multicastCoordination Entity (MCE), relay node, access point, radio access point,Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node(e.g., MME, SON node, a coordinating node, positioning node, MDT node,etc.), or even an external node (e.g., 3rd party node, a node externalto the current network), etc. It may also include, in some cases,Operations Support System (OSS), Operations and Maintenance (O&M),Self-Organizing Network (SON), positioning node, Evolved Serving MobileLocation Center (E-SMLC), a centralized controller, a core network node,Mobility Management Entity (MME), base station controller, or networkcontroller.

The network node 30 includes a communication interface circuit 38 thatincludes circuitry for communicating with other nodes in the corenetwork, radio nodes, and/or other types of nodes in the network for thepurposes of providing data and cellular communication services. Thenetwork node 30 communicates with UEs via antennas 34 and a transceivercircuit 36. The transceiver circuit 36 may include transmitter circuits,receiver circuits, and associated control circuits that are collectivelyconfigured to transmit and receive signals according to a radio accesstechnology, for the purposes of providing cellular communicationservices. According to various embodiments, cellular communicationservices may be operated according to any one or more of the 3GPPcellular standards, GSM, general packet radio service (GPRS), widebandcode division multiple access (WCDMA), high-speed downlink packet access(HSDPA), LTE and LTE-Advanced.

The network node 30 also includes one or more processing circuits 32that are operatively associated with the communication interface circuit38 or transceiver circuit 36. The network node 30 uses the communicationinterface circuit 38 to communicate with network nodes and thetransceiver 36 to communicate with UEs. For ease of discussion, the oneor more processing circuits 32 are referred to hereafter as “theprocessing circuit 32.” The processing circuit 32 comprises one or moredigital processors 42, e.g., one or more microprocessors,microcontrollers, Digital Signal Processors (DSPs), Field ProgrammableGate Arrays (FPGAs), Complex Programmable Logic Devices (CPLDs),Application Specific Integrated Circuits (ASICs), or any mix thereof.More generally, the processing circuit 32 may comprise fixed circuitry,or programmable circuitry that is specially configured via the executionof program instructions implementing the functionality taught herein, ormay comprise some mix of fixed and programmed circuitry. The processor42 may be multi-core having two or more processor cores utilized forenhanced performance, reduced power consumption, and more efficientsimultaneous processing of multiple tasks.

The processing circuit 32 also includes a memory 44. The memory 44, insome embodiments, stores one or more computer programs 46 and,optionally, configuration data 48. The memory 44 provides non-transitorystorage for the computer program 46 and it may comprise one or moretypes of computer-readable media, such as disk storage, solid-statememory storage, or any mix thereof. By way of non-limiting example, thememory 44 comprises any one or more of SRAM, DRAM, EEPROM, and FLASHmemory, which may be in the processing circuit 32 and/or separate fromthe processing circuit 32.

In general, the memory 44 comprises one or more types ofcomputer-readable storage media providing non-transitory storage of thecomputer program 46 and any configuration data 48 used by the networknode 30. Here, “non-transitory” means permanent, semi-permanent, or atleast temporarily persistent storage and encompasses both long-termstorage in non-volatile memory and storage in working memory, e.g., forprogram execution.

FIG. 3 illustrates a diagram of a wireless device, such as a userequipment 50, according to some embodiments. To ease explanation, theuser equipment 50 may also be considered to represent any wirelessdevice that may utilize CA or LAA in a network. The UE may be a radiocommunication device, target device (device targeted for communication),device to device (D2D) UE, machine type UE or UE capable of machine tomachine communication (M2M), a sensor equipped with UE, iPAD, Tablet,mobile terminals, smart phone, laptop embedded equipped (LEE), laptopmounted equipment (LME), USB dongles, Customer Premises Equipment (CPE)etc.

The user equipment 50 communicates with a radio node or base station,such as network access node 30, via antennas 54 and a transceivercircuit 56. The transceiver circuit 56 may include transmitter circuits,receiver circuits, and associated control circuits that are collectivelyconfigured to transmit and receive signals according to a radio accesstechnology, for the purposes of providing cellular communicationservices. According to various embodiments, cellular communicationservices may be operated according to any one or more of the 3GPPcellular standards, GSM, GPRS, WCDMA, HSDPA, LTE and LTE-Advanced.

The user equipment 50 also includes one or more processing circuits 52that are operatively associated with the radio transceiver circuit 56.The processing circuit 52 comprises one or more digital processingcircuits, e.g., one or more microprocessors, microcontrollers, DSPs,FPGAs, CPLDs, ASICs, or any mix thereof. More generally, the processingcircuit 52 may comprise fixed circuitry, or programmable circuitry thatis specially adapted via the execution of program instructionsimplementing the functionality taught herein, or may comprise some mixof fixed and programmed circuitry. The processing circuit 52 may bemulti-core.

The processing circuit 52 also includes a memory 64. The memory 64, insome embodiments, stores one or more computer programs 66 and,optionally, configuration data 68. The memory 64 provides non-transitorystorage for the computer program 66 and it may comprise one or moretypes of computer-readable media, such as disk storage, solid-statememory storage, or any mix thereof. By way of non-limiting example, thememory 64 comprises any one or more of SRAM, DRAM, EEPROM, and FLASHmemory, which may be in the processing circuit 52 and/or separate fromprocessing circuit 52. In general, the memory 64 comprises one or moretypes of computer-readable storage media providing non-transitorystorage of the computer program 66 and any configuration data 68 used bythe user equipment 50.

In some embodiments, the processor 62 of the processing circuit 52 mayexecute a computer program 66 stored in the memory 64 that alsoconfigures the processor 62 to perform steps for each of a plurality ofscheduled uplink transmission opportunities. These steps includeevaluating a condition regarding a number of downlink receptions withinan evaluation period preceding the scheduled uplink transmissionopportunity and selectively adjusting or not adjusting the timing, foreach scheduled uplink transmission opportunity, based on the evaluating.

In some embodiments, the processor 62 of the processing circuit 52 mayexecute a computer program 66 stored in the memory 64 that configuresthe processor 62 to perform steps for each of a plurality of scheduleduplink transmission opportunities at which the timing is adjusted. Thesesteps include determining an accuracy of an estimated downlink timingand scaling or adapting an adjustment to the timing based on thedetermined accuracy.

FIG. 4 illustrates a method 600 for maintaining timing associated withuplink transmissions that may be performed by a wireless device such asUE 50, according to some embodiments. The method 600 includes, for eachof a plurality of scheduled uplink transmission opportunities:evaluating a condition regarding a number of downlink receptions withinan evaluation period preceding the scheduled uplink transmissionopportunity (block 602) and selectively adjusting or not adjusting thetiming, for each scheduled uplink transmission opportunity, based on theevaluating (block 604).

Evaluating the condition may include determining whether at least apredetermined number N of downlink receptions on a given carrier orcarriers have been received within an evaluation period of apredetermined duration T, and wherein selectively adjusting or notadjusting the timing comprises adjusting the timing in response to thecondition being met and refraining from adjusting the timing in responseto the condition not being met. T may be expressed in terms of a numberof symbols, or a number of time slots, or a number of subframescontaining discovery reference signals.

In some cases, N or T, or both, depend on channel conditions or channelcharacteristics. In some cases, N or T, or both, depend one or more of:a channel bandwidth; a multipath delay profile; an estimated speed ofthe wireless device; an estimated Doppler shift of received signals forthe wireless device; and a received signal quality. In other cases, N orT, or both, are based on configuration information received in adownlink transmission.

Evaluating the condition may also include determining whether at least apredetermined number N of downlink receptions of a given type or types,on a given carrier or carriers, have been received within the evaluationperiod. The given type or types may include a discovery referencesignal; a cell-specific reference signal; a primary synchronizationsignal; and a secondary synchronization signal.

The method 600 may further include, for each of one or more scheduleduplink transmission opportunities at which the timing is adjusted:determining an accuracy of an estimated downlink timing, and scaling oradapting an adjustment to the timing based on the determined accuracy.Determining the accuracy of the estimated timing may be based on anumber of downlink transmissions received in a predetermined evaluationinterval preceding the adjustment. The scaling or adapting may be basedon an estimated quality of a downlink channel.

When considering the advantages of the techniques illustrated in FIG. 4,it will be appreciated that uplink transmission timing in a UE iscalculated using the downlink reception timing the UE perceives asreference. A benefit of the method shown in FIG. 4 is that the UEensures that the uplink transmission is only adjusted in case the UE hasreceived a certain number of downlink receptions during an evaluationperiod, which indirectly indicates that the accuracy of the downlinktiming is accurate. If the UE were to adjust the uplink timing based onan inaccurate downlink timing, the adjustment may be erroneous and hencecould result in that the uplink transmissions are received outside theeNB's reception window.

FIG. 5 illustrates another method 700 for maintaining timing associatedwith uplink transmissions that may be performed by a wireless devicesuch as UE 50, according to some embodiments. The method 700 includes,for each of a plurality of scheduled uplink transmission opportunitiesat which the timing is adjusted: determining an accuracy of an estimateddownlink timing (block 702) and scaling or adapting an adjustment to thetiming based on the determined accuracy (block 704). Determining theaccuracy of the estimated timing may be based on a number of downlinktransmissions received in a predetermined evaluation interval precedingthe adjustment. The scaling or adapting may be based on an estimatedquality of a downlink channel.

When considering the advantages of the technique illustrated in FIG. 5,it will again be appreciated that the uplink transmission timing in a UEis calculated using the downlink reception timing the UE perceives asreference. Scaling or adapting an adjustment of the timing depending onthe accuracy of the estimated downlink timing allows the UE to perform asmaller adjustment when the UE considers the estimated timing to not becompletely accurate. This way the risks for erronous timing adjustmentsby the UE and for the uplink transmission to reach the eNB outside theeNBs reception window are reduced. Also, when the UE performs smallertiming adjustments, there is a higher likelihood that the eNB, bysending a timing advance command to the UE, will be able to correct anyerronous timing adjustments by the UE.

It should be noted that the UE would only need to autonomously updatethe uplink transmission timing with a certain periodicity if the errorbetween the expected uplink transmission timing and the actualtransmission timing is large enough. A description of when the UE has toperform uplink transmission timing updates is defined in 3GPP TS 36.133v13.2.0 section 7.1. This means that the UE will not always update thetiming when one or more of the conditions described below are not met.These embodiments may also be combined with other embodiments discussedherein.

Furthermore, the UE behavior may be also adapted to increase theprobability that the conditions are met. For example, the downlinkreference may be adaptively selected so that the obtained downlinktiming estimate is more accurate and at least a certain minimum numberof downlink transmissions are available.

Further, the network node (e.g., eNB) may also adapt scheduling a UE'suplink transmissions based on the conditions, such as selectivelyscheduling on a carrier frequency that minimizes the uplink timingissue.

Some embodiments may involve conditioning a timing update on a number ofdownlink transmissions. In LAA, the network node may also need toperform an LBT procedure on LAA carriers before downlink transmissionson those carriers. This means that the network node may need to suppresstransmissions in case it determines that the channel is busy. Hence, theUE may not receive downlink transmissions in a timely manner in a timeresource (e.g., slot, symbol, subframe, etc.), since the network nodemay have suppressed, delayed or avoided the downlink transmissions.

While, in this instance, the suppression of transmissions by the networknode due to LBT is used as an example, it should be appreciated thatthere may be other scenarios in which the network node does not performany transmission during certain time resources. For example, in case ofa lean carrier where no or reduced number of reference signals aretransmitted, the network node may refrain from performing certaintransmissions which are used by the UE to, among other operations, tracktiming.

In some scenarios, the UE may only update the uplink transmission timingif the UE has received a certain number of downlink receptions during acertain time window T. T is also interchangeably called a time period,time duration, evaluation period, etc. For example, the UE may onlyupdate the uplink transmission timing if the UE has received at least Nnumber of downlink transmissions during a time window T. Based on thisrule, when the UE updates its uplink transmit timing, the UE willevaluate whether it has received at least N number of downlinktransmissions within the last time window T. If that is true, then theUE will perform the uplink transmission timing adjustment. Otherwise, itwill not perform any adjustment.

The parameters N and T can be expressed in terms of one or more timeresources. Examples of time resources are symbols, time slots,transmission time intervals (TTI), interleaving times, subframes,partial or half subframes, radio frames, etc. The parameter N may alsobe expressed in terms of a number of downlink transmissions comprising acertain type of signal, such as discovery reference signals (DRS), CRSsignals, PSS/SSS signals, broadcast signals, reference signals, etc. Asan example, N may be expressed in terms of number of symbols, time slotsor subframes containing DRS signals.

Example values of N and T are 1 subframe and 40 subframes, respectively.Another example of values for N and T are 2 subframes and 80 subframes.

In one example, N and/or T may be pre-defined or determined based on arule. In another example, the network node (e.g., eNB) may configure theUE with the values N and/or T. In a further example, the pre-definedrule can be based on channel conditions or characteristics. In yetanother example, the network node may base or determine theconfiguration of these parameter values on one or more channelconditions or channel characteristics. Examples of channel conditions orchannel characteristics are: channel bandwidth (e.g. downlink cell BW,uplink cell, uplink transmission BW, etc.); radio channelcharacteristics (e.g. Doppler speed of UE, multipath delay profile,channel coherence BW, etc.); and signal quality. Examples of signalquality are SINR, SNR, RSRP, RSSI, RSRQ, pathloss, RS-SINR, BLER, etc.

For example, if downlink channel BW is below a threshold (e.g., below 3MHz), then the values of N and/or T are required to be above certainrespective thresholds. Otherwise, the values of N and/or T can be equalto their respective thresholds.

In another example, under poor radio conditions the values of N and/or Tare required to be above certain respective thresholds. Examples of poorradio conditions are when Doppler speed is above a threshold (e.g.,above 70 Hz), multipath delay profile is above a threshold (e.g., above1 μs), etc.

In yet another example, if the SINR if below a certain value the UE mayuse one set of N and/or T, while if the SINR is above a certainthreshold the UE may use another set of N and/or T.

The values of parameters N and/or T may also depend on the UE's activitystate or activity level. The UE activity may be determined based onwhether the UE is in DRX, in non-DRX, or whether the DRX cycle length isbelow a certain threshold or not.

The UE may also scale the amount of the uplink transmission timingadjustment based on the number of received downlink transmissions.

The UE may apply one or any combination of the conditions whendetermining whether to update the uplink transmission timing. Forexample, the UE may update the uplink transmission timing if at least N′number of downlink samples or signals or transmissions have beenreceived during a time T′, where these samples or received signals areabove a certain channel quality threshold, or when N available samplesare above a threshold. This allows the UE to update the uplinktransmission timing only if the UE has acquired a certain number ofsamples which have a certain quality.

In a further embodiment, whether the UE is to apply one or moreconditions, and also which one or more of the plurality of conditions tobe applied for uplink timing adjustment, may be configured by thenetwork node. This may be indicated by the eNB via RRC signaling. Thisconfiguration may be applicable on a per-carrier basis or on aper-Timing Advance Group basis, or for any group of carriers. Theconfiguration information may be signaled to the UE by means of a flagor an indicator per carrier or per TAG or per group of carriers. Forexample, the conditions can be pre-defined and the signaled indicator(s)represents the identifier of the condition to be used by the UE. Thisallows the network node to configure the UE to apply this behavior oncertain carriers and/or in certain scenarios. For example, it may not bevaluable to apply these conditions for carriers which do not requireLBT. Even if LBT is applied to a certain carrier but the load (e.g.,number of nodes using carrier, interference, etc.) on the carrier isbelow a threshold, then the LBT may often succeed on that carrier. Forinstance, a channel will be considered free such that the eNB/UE cantransmit on that carrier.

Another alternative is that the UE selects whether and which conditionsto apply based on a pre-defined or a pre-configured rule. This may, forexample, be specified in a specification. One example rule is that theUE would apply one or more of the conditions on LAA-carriers based onwhether it can be determined that a carrier is an LAA-carrier. Thisdetermination may be based on whether it operates using certain type offrame structure. As an example, it can be frame structure 3 (3GPP TS36.211) and/or the eNB has configured certain parameters for thatcarrier (e.g., laa-SCellConfiguration). Another example rule is that theUE would apply one or more of the conditions on carriers on certainfrequency band(s), such as in the range of 5-6 GHz, LTE band number 46,etc.

Some embodiments may involve a method in a UE for partial uplinktransmission timing adjustment that is based on downlink signalreception accuracy. In an example, the UE will determine the accuracy ofthe downlink timing and based on this, determine if and how much the UEshall update the uplink transmission timing. The accuracy of thedownlink timing in turn depends on the number of downlink transmissionreceived by the UE, such as the number of downlink subframes with DRSover certain time period. For instance, if the UE has received only afewer downlink time resources (e.g., downlink subframes with DRS belowthreshold) recently (or to use the formulations from above; N is smallerthan threshold for the past time T), then the accuracy of the downlinktiming determined by the UE may be worse than an accuracy threshold,such as worse than ±24 Ts, where 1 Ts=32.55 ns. In this scenario, the UEmay perform a partial uplink transmission timing adjustment, such asupdating the uplink timing with a smaller amount than it would adjustthe uplink timing, if the determined downlink timing accuracy is notworse than the accuracy threshold. The UE may apply a certain thresholdfor N and T for determining when the accuracy is considered high andwhen it is considered low. For example, if N is less than 2 downlinksubframes and/or Tis above 80 ms, then the UE may assume that theaccuracy of the downlink timing estimated by the UE is worse than thethreshold (e.g., larger than the magnitude of ±24 Ts).

In yet another example, the UE may adapt the uplink timing adjustmentvalue based on a parameter related to the estimated accuracy of thedownlink timing. That is, the amount of uplink transmission timingadjustment may be scaled or adapted by the number of successfullyreceived downlink transmissions over the past time period T. Forexample, if during the time period T the UE can receive at most N_(max)number of downlink receptions, but the UE actually receive N_(received)number of downlink receptions, then the UE may update the uplinktransmission timing with a size S expressed in time, such as between ±12Ts to ±24 Ts. In general, S can be expressed as a function of S_(max),N_(received) and N_(max), such as S=f(S_(max), N_(received), N_(max)).More specifically, S can be expressed by the following relation:

S=S _(max)*(N _(received) /N _(max)).

The UE may also consider the quality of the channel when determining theamount of the timing adjustment. The UE may scale the adjustment stepsize with a value X, which is calculated as a function of the estimatedquality of the channel, such as S=S_(max)*f(Channel quality). Note thatthe function may not be limited to only considering the quality of thechannel.

FIG. 6 illustrates an example functional module or circuit architectureas may be implemented in the user equipment 50, e.g., based on thetransmit timing maintenance circuitry 60. The illustrated embodiment atleast functionally includes an evaluating module 1002 for evaluating,for each of a plurality of scheduled LBT transmission opportunities, acondition regarding a number of downlink receptions within an evaluationperiod preceding the scheduled uplink transmission opportunity. Theimplementation also includes an adjusting module 1004 for selectivelyadjusting or not adjusting the timing, for each scheduled uplinktransmission opportunity, based on the evaluating.

FIG. 7 illustrates another example functional module or circuitarchitecture as may be implemented in the user equipment 50, e.g., basedon the transmit timing maintenance circuitry 60. The illustratedembodiment at least functionally includes, for each of a plurality ofscheduled LBT transmission opportunities at which the timing isadjusted, a determining module 1102 for determining an accuracy of anestimated downlink timing and an adapting module 1104 for scaling oradapting an adjustment to the timing based on the determined accuracy.

While it would be desirable to account for results from LBT assessmentto determine whether to adjust timing associated with uplinktransmission, in some UE architectures/implementations, the moduleperforming the LBT may be located close to the antenna in the UE. Thiscan mean that the LBT procedure is one of the last procedures performedby the UE before the transmission. Due to this module location, it maynot be possible for other mechanisms in the UE, that are applied orperformed prior to the LBT procedure, to take the outcome of the LBTevaluation into account. For example, the Medium Access Control (MAC)layer may be unable to take one action for the case when the channel isbusy and another action when the channel is free. This is because someMAC operations may be performed prior to LBT being evaluated, as it maynot be feasible to first evaluate LBT and then, based on the outcome,take different actions in MAC. The reason why this may not be feasibleis that LBT operates on a very short time-frame—thus, the time from whenthe UE has sensed/“listened” to the channel until that the UE transmitsmay be very short and the UE may not be able to perform MAC processingin the short time between sensing and transmission.

In the case of uplink transmission timing handling, it may be thatcertain mechanisms or functions are performed by an entity higher up orearlier in the UE's radio structure. (Here, “entity” refers to afunctional module, which may be implemented by a processor executingprogram instructions, or by digital logic, or by some combinationthereof.) This means that this entity may not know whether (due to LBT)the channel is considered free or busy when doing the uplinktransmission timing adjustments.

For such UE architectures, in some embodiments, the uplink transmissiontiming handling entity assumes that a planned transmission will succeed(i.e., that the transmission will be performed) and will thus update theuplink transmission timing according to the defined rules (e.g. asdescribed in connection with FIGS. 4 and 5). However, if it turns outthat the channel was busy (and hence that the UE could not successfullyperform the transmission), then the uplink transmission timing handlingentity is made aware of this after LBT has been performed, in theseembodiments. This notification may be implemented by an indication sentfrom the LBT-entity to the entity handling uplink transmission timing.In some cases, the indication is sent from the LBT-entity to the uplinktransmission timing handling entity only in a case of a failedtransmission, but not in a case of a successful transmission. Absence ofthe indication may indicate a successful transmission. Or vice-versa, anindication may only be sent in a case where the LBT entity successfullytransmits, in some embodiments, in which case the absence of anindication implicitly means that the channel was busy.

The uplink transmission timing handling entity may, based on theindications from the LBT-entity, determine whether LBT was successful ornot. Based on whether the UE performed the transmission, the uplinktransmission handling entity reverts the uplink transmission timing tothe timing that the UE should have applied in case no transmission tookplace.

In another example, instead of making an assumption about the successfultransmission, the uplink transmission timing adjustment may be appliedbased on the UE LBT success history or the estimated likelihood the UELBT success.

Accordingly, FIG. 8 illustrates an example method 1200 that may beimplemented in a wireless device, such as by the processing circuit 52in UE 50, for maintaining timing associated with uplink transmissions.The method 1200 includes: determining, for each of a plurality ofscheduled LBT transmission opportunities, whether an error in a currentuplink transmission timing, with respect to a reference point based on adownlink timing for a reference cell, exceeds a predetermined threshold(block 1202). The method further comprises adjusting the timingassociated with uplink transmissions, for each scheduled LBTtransmission opportunity for which the error exceeds the predeterminedthreshold (block 1204). The method 1200 also includes performing an LBTassessment to determine whether the wireless device is permitted totransmit in the scheduled LBT transmission opportunity (block 1206), foreach of the plurality of scheduled LBT transmission opportunities, andfor each scheduled LBT transmission opportunity in which the LBTassessment indicates that the wireless device is not permitted totransmit, reversing any adjustment to the timing associated with uplinktransmissions made for that scheduled LBT transmission opportunity(block 1208).

FIG. 9 illustrates another example method 1300 that may be implementedin a wireless device, such as by the processing circuit 52 in UE 50, formaintaining timing associated with uplink transmissions. The method 1300includes: determining, for each of a plurality of scheduled LBTtransmission opportunities, whether an error in a current uplinktransmission timing, with respect to a reference point based on adownlink timing for a reference cell, exceeds a predetermined threshold(block 1302), The method further includes selectively adjusting thetiming associated with uplink transmissions, for each scheduled LBTtransmission opportunity for which the error exceeds the predeterminedthreshold, based on an estimated likelihood of LBT success (block 1304).The estimated likelihood of LBT success may be based on a history of LBTsuccesses and failures. The method 1300 also includes performing an LBTassessment, for each of the plurality of scheduled LBT transmissionopportunities, to determine whether the wireless device is permitted totransmit in the scheduled LBT transmission opportunity (block 1306), andfor each scheduled LBT transmission opportunity in which the LBTassessment indicates that the wireless device is not permitted totransmit, reversing any adjustment to the timing associated with uplinktransmissions made for that scheduled LBT transmission opportunity(block 1308).

FIG. 10 illustrates another example functional module or circuitarchitecture as may be implemented in the user equipment 50, e.g., basedon the transmit timing maintenance circuitry 60. The illustratedembodiment at least functionally includes a determining module 1402 fordetermining, for each of a plurality of scheduled LBT transmissionopportunities, whether an error in a current uplink transmission timing,with respect to a reference point based on a downlink timing for areference cell, exceeds a predetermined threshold, and an adjustingmodule 1404 for adjusting the timing associated with uplinktransmissions, for each scheduled LBT transmission opportunity for whichthe error exceeds the predetermined threshold. The functionalimplementation for each of a plurality of scheduled LBT transmissionopportunities also includes a performing module 1406 for performing anLBT assessment, for each of the plurality of scheduled LBT transmissionopportunities, to determine whether the wireless device is permitted totransmit in the scheduled LBT transmission opportunity, and a reversingmodule 1408 for, for each scheduled LBT transmission opportunity inwhich the LBT assessment indicates that the wireless device is notpermitted to transmit, reversing any adjustment to the timing associatedwith uplink transmissions made for that scheduled LBT transmissionopportunity (block 1208). In another example implementation, theadjusting module 1404 is for selectively adjusting the timing associatedwith uplink transmissions, for each scheduled LBT transmissionopportunity for which the error exceeds the predetermined threshold,based on an estimated likelihood of LBT success.

Example embodiments may include:

-   1. A method, in a wireless device, for maintaining timing associated    with uplink transmissions, the method comprising, for each of a    plurality of scheduled listen-before-talk (LBT) transmission    opportunities:    -   determining whether an error in a current uplink transmission        timing, with respect to a reference point based on a downlink        timing for a reference cell, exceeds a predetermined threshold;    -   adjusting the timing associated with uplink transmissions, for        each scheduled LBT transmission opportunity for which the error        exceeds the predetermined threshold;    -   performing an LBT assessment to determine whether the wireless        device is permitted to transmit in the scheduled LBT        transmission opportunity; and    -   for each scheduled LBT transmission opportunity in which the LBT        assessment indicates that the wireless device is not permitted        to transmit, reversing any adjustment to the timing associated        with uplink transmissions made for that scheduled LBT        transmission opportunity.-   2. A method, in a wireless device, for maintaining timing associated    with uplink transmissions, the method comprising, for each of a    plurality of scheduled listen-before-talk (LBT) transmission    opportunities:    -   determining whether an error in a current uplink transmission        timing, with respect to a reference point based on a downlink        timing for a reference cell, exceeds a predetermined threshold;    -   for each scheduled LBT transmission opportunity for which the        error exceeds the predetermined threshold, selectively adjusting        the timing associated with uplink transmissions, based on an        estimated likelihood of LBT success;    -   performing an LBT assessment to determine whether the wireless        device is permitted to transmit in the scheduled LBT        transmission opportunity.-   3. The method of embodiment 2, wherein the method further comprises    for each scheduled LBT transmission opportunity in which the LBT    assessment indicates that the wireless device is not permitted to    transmit, reversing any adjustment to the timing associated with    uplink transmissions made for that scheduled LBT transmission    opportunity-   4. The method of embodiment 2 or 3, wherein the estimated likelihood    of LBT success is based on a history of LBT successes and failures.-   5. A wireless device adapted to carry out a method according to any    of embodiments 1 to 4.-   6. A wireless device configured to maintain timing associated with    uplink transmissions, comprising a processing circuit configured to,    for each of a plurality of scheduled listen-before-talk (LBT)    transmission opportunities:    -   determine whether an error in a current uplink transmission        timing, with respect to a reference point based on a downlink        timing for a reference cell, exceeds a predetermined threshold;    -   adjust the timing associated with uplink transmissions, for each        scheduled LBT transmission opportunity for which the error        exceeds the predetermined threshold;    -   perform an LBT assessment to determine whether the wireless        device is permitted to transmit in the scheduled LBT        transmission opportunity; and    -   for each scheduled LBT transmission opportunity in which the LBT        assessment indicates that the wireless device is not permitted        to transmit, reverse any adjustment to the timing associated        with uplink transmissions made for that scheduled LBT        transmission opportunity.-   7. A wireless device configured to maintain timing associated with    uplink transmissions, comprising a processing circuit configured to,    for each of a plurality of scheduled listen-before-talk (LBT)    transmission opportunities:    -   determine whether an error in a current uplink transmission        timing, with respect to a reference point based on a downlink        timing for a reference cell, exceeds a predetermined threshold;    -   for each scheduled LBT transmission opportunity for which the        error exceeds the predetermined threshold, selectively adjust        the timing associated with uplink transmissions, based on an        estimated likelihood of LBT success;    -   perform an LBT assessment to determine whether the wireless        device is permitted to transmit in the scheduled LBT        transmission opportunity.-   8. The wireless device of embodiment 7, wherein the processing    circuit is further configured to, for each scheduled LBT    transmission opportunity in which the LBT assessment indicates that    the wireless device is not permitted to transmit, reverse any    adjustment to the timing associated with uplink transmissions made    for that scheduled LBT transmission opportunity.-   9. The wireless device of embodiment 7 or 8, wherein the estimated    likelihood of LBT success is based on a history of LBT successes and    failures.-   10. A non-transitory computer readable storage medium storing a    computer program for maintaining timing associated with uplink    transmissions comprising program instructions that, when executed on    a wireless device configured to operate in a wireless communication    network, cause the processing circuit to, for each of a plurality of    scheduled listen-before-talk (LBT) transmission opportunities:    -   determine whether an error in a current uplink transmission        timing, with respect to a reference point based on a downlink        timing for a reference cell, exceeds a predetermined threshold;    -   adjust the timing associated with uplink transmissions, for each        scheduled LBT transmission opportunity for which the error        exceeds the predetermined threshold;    -   perform an LBT assessment to determine whether the wireless        device is permitted to transmit in the scheduled LBT        transmission opportunity; and    -   for each scheduled LBT transmission opportunity in which the LBT        assessment indicates that the wireless device is not permitted        to transmit, reverse any adjustment to the timing associated        with uplink transmissions made for that scheduled LBT        transmission opportunity.-   11. A non-transitory computer readable storage medium storing a    computer program for maintaining timing associated with uplink    transmissions comprising program instructions that, when executed on    a wireless device configured to operate in a wireless communication    network, cause the processing circuit to, for each of a plurality of    scheduled listen-before-talk (LBT) transmission opportunities:    -   determine whether an error in a current uplink transmission        timing, with respect to a reference point based on a downlink        timing for a reference cell, exceeds a predetermined threshold;    -   for each scheduled LBT transmission opportunity for which the        error exceeds the predetermined threshold, selectively adjust        the timing associated with uplink transmissions, based on an        estimated likelihood of LBT success;    -   perform an LBT assessment to determine whether the wireless        device is permitted to transmit in the scheduled LBT        transmission opportunity.-   12. A computer program, comprising instructions which, when executed    on at least one processing circuit, cause the at least one    processing circuit to carry out the method according to any one of    embodiments 1 to 4.-   13. A carrier containing the computer program of embodiment 12,    wherein the carrier is one of an electronic signal, optical signal,    radio signal, or computer readable storage medium.-   14. A wireless device comprising, for each of a plurality of    scheduled LBT transmission opportunities:    -   a determining module for determining whether an error in a        current uplink transmission timing, with respect to a reference        point based on a downlink timing for a reference cell, exceeds a        predetermined threshold;    -   an adjusting module for adjusting the timing associated with        uplink transmissions, for each scheduled LBT transmission        opportunity for which the error exceeds the predetermined        threshold;    -   a performing module for performing an LBT assessment to        determine whether the wireless device is permitted to transmit        in the scheduled LBT transmission opportunity; and    -   a reversing module for, for each scheduled LBT transmission        opportunity in which the LBT assessment indicates that the        wireless device is not permitted to transmit, reversing any        adjustment to the timing associated with uplink transmissions        made for that scheduled LBT transmission opportunity.-   15. A wireless device comprising, for each of a plurality of    scheduled LBT transmission opportunities:    -   a determining module for determining whether an error in a        current uplink transmission timing, with respect to a reference        point based on a downlink timing for a reference cell, exceeds a        predetermined threshold;    -   an adjusting module for, for each scheduled LBT transmission        opportunity for which the error exceeds the predetermined        threshold, selectively adjusting the timing associated with        uplink transmissions, based on an estimated likelihood of LBT        success; and    -   a performing module for performing an LBT assessment to        determine whether the wireless device is permitted to transmit        in the scheduled LBT transmission opportunity.-   16. The wireless device of embodiment 15 further comprising a    reversing module for, for each scheduled LBT transmission    opportunity in which the LBT assessment indicates that the wireless    device is not permitted to transmit, reversing any adjustment to the    timing associated with uplink transmissions made for that scheduled    LBT transmission opportunity.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

1-17. (canceled)
 18. A method, in a wireless device, for maintainingtiming associated with uplink transmissions, the method comprising, foreach of a plurality of scheduled listen-before-talk (LBT) transmissionopportunities: determining whether an error in a current uplinktransmission timing, with respect to a reference point based on adownlink timing for a reference cell, exceeds a predetermined threshold;adjusting the timing associated with uplink transmissions, for eachscheduled LBT transmission opportunity for which the error exceeds thepredetermined threshold; performing an LBT assessment to determinewhether the wireless device is permitted to transmit in the scheduledLBT transmission opportunity; and for each scheduled LBT transmissionopportunity in which the LBT assessment indicates that the wirelessdevice is not permitted to transmit, reversing any adjustment to thetiming associated with uplink transmissions made for that scheduled LBTtransmission opportunity.
 19. A method, in a wireless device, formaintaining timing associated with uplink transmissions, the methodcomprising, for each of a plurality of scheduled listen-before-talk(LBT) transmission opportunities: determining whether an error in acurrent uplink transmission timing, with respect to a reference pointbased on a downlink timing for a reference cell, exceeds a predeterminedthreshold; for each scheduled LBT transmission opportunity for which theerror exceeds the predetermined threshold, selectively adjusting thetiming associated with uplink transmissions, based on an estimatedlikelihood of LBT success; and performing an LBT assessment to determinewhether the wireless device is permitted to transmit in the scheduledLBT transmission opportunity.
 20. The method of claim 19, furthercomprising for each scheduled LBT transmission opportunity in which theLBT assessment indicates that the wireless device is not permitted totransmit, reversing any adjustment to the timing associated with uplinktransmissions made for that scheduled LBT transmission opportunity. 21.The method of claim 19, wherein the estimated likelihood of LBT successis based on a history of LBT successes and failures.
 22. A wirelessdevice configured to maintain timing associated with uplinktransmissions, the wireless device comprising a processing circuitconfigured to, for each of a plurality of scheduled listen-before-talk(LBT) transmission opportunities: determine whether an error in acurrent uplink transmission timing, with respect to a reference pointbased on a downlink timing for a reference cell, exceeds a predeterminedthreshold; adjust the timing associated with uplink transmissions, foreach scheduled LBT transmission opportunity for which the error exceedsthe predetermined threshold; perform an LBT assessment to determinewhether the wireless device is permitted to transmit in the scheduledLBT transmission opportunity; and for each scheduled LBT transmissionopportunity in which the LBT assessment indicates that the wirelessdevice is not permitted to transmit, reverse any adjustment to thetiming associated with uplink transmissions made for that scheduled LBTtransmission opportunity.
 23. A wireless device configured to maintaintiming associated with uplink transmissions, the wireless devicecomprising a processing circuit configured to, for each of a pluralityof scheduled listen-before-talk (LBT) transmission opportunities:determine whether an error in a current uplink transmission timing, withrespect to a reference point based on a downlink timing for a referencecell, exceeds a predetermined threshold; for each scheduled LBTtransmission opportunity for which the error exceeds the predeterminedthreshold, selectively adjust the timing associated with uplinktransmissions, based on an estimated likelihood of LBT success; andperform an LBT assessment to determine whether the wireless device ispermitted to transmit in the scheduled LBT transmission opportunity. 24.The wireless device of claim 23, wherein the processing circuit isfurther configured to, for each scheduled LBT transmission opportunityin which the LBT assessment indicates that the wireless device is notpermitted to transmit, reverse any adjustment to the timing associatedwith uplink transmissions made for that scheduled LBT transmissionopportunity.
 25. The wireless device of claim 23, wherein the estimatedlikelihood of LBT success is based on a history of LBT successes andfailures.
 26. A non-transitory computer-readable medium comprising,stored thereupon, a computer program comprising instructions that, whenexecuted on at least one processing circuit of a wireless device, causethe at least one processing circuit to, for each of a plurality ofscheduled listen-before-talk (LBT) transmission opportunities: determinewhether an error in a current uplink transmission timing, with respectto a reference point based on a downlink timing for a reference cell,exceeds a predetermined threshold; adjust the timing associated withuplink transmissions, for each scheduled LBT transmission opportunityfor which the error exceeds the predetermined threshold; perform an LBTassessment to determine whether the wireless device is permitted totransmit in the scheduled LBT transmission opportunity; and for eachscheduled LBT transmission opportunity in which the LBT assessmentindicates that the wireless device is not permitted to transmit, reverseany adjustment to the timing associated with uplink transmissions madefor that scheduled LBT transmission opportunity.